1. Field of the Invention
The present invention relates to an adhesive, a bonding method and an assembly of a mounting substrate. More specifically, the present invention relates to a mixed adhesive comprising a redox polymerization-type acrylic adhesive and an epoxy adhesive, a bonding method using the same and an assembly of a mounti ng substrate. The adhesive and the bondi ng method according to the present invention can used to substitute a soldering method, and are especially useful to bond functional elements such as various electronic parts on a mounting substrate such as a wiring circuit substrate, a printed wiring substrate or the like.
2.Description of Related Art
In recent years, a semiconductor technology has been markedly developed. Functional elements such as high-performance IC, LSI and the like have been developed one after another, and the mass production has been continued. As a bonding method for mounting these functional elements on a mounting substrate, a soldering method has been known. However, according to the development of the semiconductor technology, various bonding methods other than the soldering method have been proposed, and are being put to practical use.
As a method other than the soldering method, a bonding method using a resin adhesive which can cope well with a fine circuit pattern formed on a mounting substrate, a working environment, an operational environment and the like and which can realize bonding with a high reliability has attracted much interest, and it has been partially put to practical use. Further, a conductive adhesive obtained by adding conductive fine particles to the above-mentioned adhesive has been known. For such an adhesive, it is required that stable bonding can be realized in which no thermal stress remains in a bonded portion after bonding.
Incidentally, when the bonding is conducted using the above-mentioned resin adhesive or conductive adhesive in place of the soldering, there are the following advantages.
That is, since a soldering material generally used in the soldering has a poor wettability with aluminum (Al) generally used as an electrode of a functional element to be bonded, a film for improving a wettability of a soldering material has to be formed in advance on the Al electrode. To this end, an extra film-forming step is required, involving a high cost. However, when the above-mentioned adhesive is used, such inconveniences are eliminated.
Further, since a melting point of a general soldering material is 183xc2x0 C., the soldering has to be conducted at a temperature of higher than 183xc2x0 C., generally higher than approximately 200xc2x0 C. For this reason, there is a problem that a bonded portion undergoes a thermal stress. However, when, for example, an epoxy adhesive is used, the curing treatment can be conducted at approximately 150xc2x0 C. which is a temperature lower than the soldering temperature. Thus, it is possible to reduce a thermal stress that the bonded portion undergoes.
A bonding method using a resin or conductive adhesive has, compared with the soldering method, a large number of advantages that, for example,
(1) a thermal stress that a bonded portion undergoes by an adhesive is lower than a thermal stress that a soldered portion undergoes by the soldering method,
(2) since the heat treatment at 200xc2x0 C. or more as in the soldering method is not required, a heater capable of heating at this temperature is dispensed with,
(3) it is unnecessary to design a mounting substrate so as to endure a high temperature, with a result that a production cost can be reduced, and
(4) the bonding can be conducted without using Pb contained in the soldering material and having an adverse effect on environment.
Nevertheless, when a functional element is bonded to a mounting substrate using an ordinary adhesive, a special device such as a press having a heating mechanism is needed. Further, a thermal stress of a bonded portion is greater than that in the bonding at room temperature, though it is less than in the soldering. Especially, when a bonded portion is soft as in a substrate made of an organic material or a mounting substrate having a photosensitive resin laminated thereon, the substrate is much deformed at a high temperature in the bonding. Consequently, the reliability of the bonded portion comes to decrease.
Thus, for further improving the reliability of the bonded portion, it is required to more reduce the thermal stress that the bonded portion undergoes. To this end, an adhesive capable of bonding at room temperature and having a good reliability is needed.
Therefore, an acrylic adhesive comprising an A agent composed mainly of a methacrylic monomer made of xcfx89-carboxy-polycaprolactone monoacrylate, an organic peroxide, a polymerization inhibitor and an elastomer and further containing an epoxy resin as a chlorine ion trapping agent and a B agent composed mainly of a reducing agent that forms a redox catalyst system with the organic peroxide of the A agent has been proposed as the above-mentioned resin adhesive capable of bonding at room temperature (Japanese Unexamined Patent Publication No. HEI 7(1995)-216310).
However, it has been known that the above-mentioned acrylic adhesive is inferior to the epoxy adhesive in an indirect fillability, a heat resistance and the like and has a low curing rate at room temperature. Accordingly, it is lacking in the reliability and the productivity as an adhesive for bonding a functional element to a mounting substrate.
It is an object of the present invention to provide, in view of the above-mentioned problems, a novel adhesive in which upon using a mixed adhesive obtained by combining a redox polymerization-type acrylic adhesive with an epoxy adhesive, a functional element can be fixed on a mounting substrate such as a wiring circuit substrate or the like at room temperature and then heat-cured to thereby minimize a thermal stress at the bonded portion and the heat resistance and the reliability of the bonded portion are excellent, a bonding method and an assembly of a mounting substrate.
Thus, according to the present invention, there is provided an adhesive comprising a two-pack adhesive of an A agent selected from components, an acrylic monomer, a peroxide, a reducing agent, an epoxy resin precursor and a curing agent and containing at least one or two of the acrylic monomer, the peroxide and the reducing agent, and a B agent containing all of the remaining components which are not selected in the A agent.
Further, according to the present invention, there is provided an adhesive comprising the adhesive is composed of anacrylicmonomer, aperoxide, areducingagent, anepoxyresin precursor and a curing agent, at least one of the acrylic monomer, the peroxide and the reducing agent being coated with a thermoplastic resin to form a microcapsule.
Still further, according to the present invention, there is provided a bonding method which is a method of bonding two members, comprising; coating an A agent selected from components, an acrylic monomer, a peroxide, a reducing agent, an epoxy resin precursor and a curing agent and containing at least one or two of the acrylic monomer, the peroxide and the reducing agent on one member, coating a B agent containing all of the remaining components which are not selected in the A agent on another member, fixing the two members so as to contact the coated surfaces, and then heat-curing the adhesive composed of the A agent and the B agent.
Furthermore, according to the present invention, there is provided a bonding method which is a method of bonding two members, comprising; coating an adhesive composed of an acrylic monomer, a peroxide, a reducing agent, fixing an epoxy resin precursor and a curing agent between the two members, the two members, and then heat-curing the adhesive.
Moreover, according to the present invention, there is provided an assembly of a mounting substrate in which pad portions of the mounting substrate and lead terminals of a functional element mounted thereon are electrically connected with an anisotropic conductive adhesive, characterized in that the anisotropic conductive adhesive is a two-pack adhesive of an A agent selected from components, an acrylic monomer, a peroxide, a reducing agent, an epoxy resin precursor, a curing agent and a microcapsule-type conductive filler obtained by coating conductive fine particles with an insulating resin and containing at least one or two of the acrylic monomer, the peroxide and the reducing agent, and a B agent containing all of the remaining components which are not selected in the A agent.
In addition, according to the present invention, there is provided an assembly of a mounting substrate in which pad portions of the mounting substrate and the lead terminals of a functional element mounted thereon are electrically connected with an anisotropic conductive adhesive, characterized in that the anisotropic conductive adhesive is an adhesive comprising an acrylic monomer, a peroxide, a reducing agent, an epoxy resin precursor, a curing agent and a microcapsule-type conductive filler obtained by coating conductive fine particles with an insulating resin, at least one of the acrylic monomer, the peroxide and the reducing agent being coated with a thermoplastic resin to form a microcapsule.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.